Mixer circuits are widely employed in radio frequency (hereinafter referred to as RF) communication systems. The expression ‘radio frequency’ is used in this specification to designate wireless communication frequencies without any specific upper limit and embodiments of this invention are usable up to millimeter wavelength frequencies and beyond. Generally speaking, mixers perform frequency translation by multiplying two signals and possibly their harmonics.
RF mixers are for instance used to convert applied RF signals to intermediate frequency (hereinafter referred to as IF) signals at the input section of an RF spectrum analyzer. Low mixer distortion and high isolation between local oscillator (hereinafter referred to as LO) signals applied to the mixer and the IF signals produced by the mixer enable an RF spectrum analyzer to accurately represent the spectral content of applied RF signals. Mixers are used to either translate or convert the frequency up, for instance when mixing an IF signal with a LO signal to produce a suitable RF signal for transmission or to translate or convert the frequency down, for instance when a received RF signal is mixed with a LO signal to produce a suitable IF signal.
RF mixers used today in the RF spectrum uses two or more mixing diodes to achieve the desired mixing with low distortion, producing complicated mechanical assemblies and unnecessary us of costly components.
U.S. Pat. No. 5,790,945 describes a dumbbell shaped resonator coupling IF signals from short transmission lines to an output transmission line at a RF mixer's IF output port. The RF mixer uses two diodes to perform the mixing of the RF and LO signals.
The use of multiple diodes generates complicated and unnecessarily expensive circuits. The diodes have a forward voltage drop when they are conducting, causing unwanted power dissipation. The forward voltage drop also limits the mixer's power handling capability.